// Copyright 2001, FreeHEP.
package org.freehep.util.io;

import java.io.IOException;
import java.io.InputStream;

/**
 * The ASCIIHexOutputStream decodes ASCII Hexadecimal. The exact definition of
 * ASCII Hex encoding can be found in the PostScript Language Reference (3rd
 * ed.) chapter 3.13.3.
 * 
 * IMPORTANT: inherits from InputStream rather than FilterInputStream so that
 * the correct read(byte[], int, int) method is used.
 * 
 * @author Mark Donszelmann
 * @version $Id: ASCIIHexInputStream.java,v 1.3 2008/05/04 12:21:59 murkle Exp $
 */
public class ASCIIHexInputStream extends InputStream {

    private boolean ignoreIllegalChars;

    private boolean endReached;

    private int prev;

    private int lineNo;

    private InputStream in;

    /**
     * Create an ASCIIHex Input Stream from given stream
     * 
     * @param input input stream to use
     */
    public ASCIIHexInputStream(InputStream input) {
        this(input, false);
    }

    /**
     * Create an ASCIIHex Input Stream from given stream and have it optionally
     * ignore illegal characters
     * 
     * @param input input stream to use
     * @param ignore ignore illegal characters
     */
    public ASCIIHexInputStream(InputStream input, boolean ignore) {
        super();
        in = input;
        ignoreIllegalChars = ignore;
        endReached = false;
        prev = -1;
        lineNo = 1;
    }

    public int read() throws IOException {
        if (endReached)
            return -1;

        int b0 = readPart();
        if (b0 == -1)
            return -1;

        int b1 = readPart();
        if (b1 == -1)
            b1 = 0;

        int d = (b0 << 4 | b1) & 0x00FF;
        return d;
    }

    /**
     * @return current line number
     */
    public int getLineNo() {
        return lineNo;
    }

    private int readPart() throws IOException, EncodingException {
        while (true) {
            int b = in.read();
            switch (b) {
            case -1:
                endReached = true;
                if (!ignoreIllegalChars) {
                    throw new EncodingException(
                            "missing '>' at end of ASCII HEX stream");
                }
                return -1;
            case '>':
                endReached = true;
                return -1;
            case '\r':
                lineNo++;
                prev = b;
                break;
            case '\n':
                if (prev != '\r') {
                    lineNo++;
                }
                prev = b;
                break;
            case ' ':
            case '\t':
            case '\f':
            case 0:
                // skip whitespace
                prev = b;
                break;
            case '0':
                return 0;
            case '1':
                return 1;
            case '2':
                return 2;
            case '3':
                return 3;
            case '4':
                return 4;
            case '5':
                return 5;
            case '6':
                return 6;
            case '7':
                return 7;
            case '8':
                return 8;
            case '9':
                return 9;
            case 'A':
            case 'a':
                return 10;
            case 'B':
            case 'b':
                return 11;
            case 'C':
            case 'c':
                return 12;
            case 'D':
            case 'd':
                return 13;
            case 'E':
            case 'e':
                return 14;
            case 'F':
            case 'f':
                return 15;
            default:
                if (!ignoreIllegalChars) {
                    throw new EncodingException("Illegal char " + b
                            + " in HexStream");
                }
                prev = b;
                break;
            }
        }
    }
}
